http://llvm.org/bugs/show_bug.cgi?id=14019
Bug #: 14019
Summary: "-S" and "-emit-llvm | llc" produce different
assembly?
Product: clang
Version: trunk
Platform: PC
OS/Version: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Driver
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Classification: Unclassified
As of r165016,
$ cat hello.c
void f() {}
void hello() {
int x;
x = 42;
f();
}
-----------
Running these three commands to generate output files:
$ clang hello.c -Xclang -triple=i386-pc-win32 -o - -S >a
$ clang -cc1 -triple=i386-pc-win32 hello.c -o - -emit-llvm | llc >b
$ clang -cc1 hello.c -triple=i386-pc-win32 -o - -emit-llvm -S >c
# FTR, the outputs don't change in the presence of "-cxx-abi microsoft".
Comparing the output:
$ diff -u a b
--- a
+++ b
@@ -17,13 +17,10 @@
.align 16, 0x90
_hello: # @hello
# BB#0: # %entry
- pushl %ebp
- movl %esp, %ebp
pushl %eax
- movl $42, -4(%ebp)
+ movl $42, (%esp)
calll _f
- addl $4, %esp
- popl %ebp
+ popl %eax
ret
$ diff -u b c
<assembly is the same, only the comments differ a bit>
-----------
Can you explain the major difference between (a) and (b,c) ?
Is it a bug or it's meant to be this way? If it's the latter - why?
What should I look at while testing what assembly Clang generates for my source
code?
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